In the past, concrete pipe sections have been connected to form drains or culverts by using a male and female type of connection such as a bell and spigot and tongue-and-groove. The spigot is a tapered end while the bell is flared. The spigot end on one pipe is inserted into the flared end on another pipe. Rubber gaskets have been placed on the spigot with the gasket rings compressed in making the joint. The joint is then filled with mortar or asphalt to seal the pipe. As the pipe settles over time, the joints tend to open as the mortar or asphalt dries out and cracks.
In order to provide a more rigid and lasting connection, sections of concrete pipe were cast with the ends of reinforcing rods projecting out of the pipe at one end and with an aperture or recess at the other end for receiving the end of the reinforcing rod from a section of pipe to be joined. The ends of the reinforcing rods were threaded and washers and threaded nuts were used to fasten the sections together. This method presents a serious problem in that the threaded ends of the reinforcing rods can be damaged in shipping or in joining sections of pipe together, destroying the usefulness of the entire section of pipe.
Other techniques have also been used, such as hook-and-eye methods; however, these also suffered like the exposed reinforcing rods from damage in shipping or in assembling pipe sections together.